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Feb. 21, 1956 J. D. BERWICK, JR 27353O4 METHOD OF EVALUATING COPPER BASEALLOYS Filed Feb. 27, 1952 OIX WW 3ZIS NIVH) INVENTOR United StatesPatent fice METHOD OF EVALUATING COPPER BASE ALLOYS John D. Berwick, Jr.North Haven, Conn., assignor to Olin Mathieson Chemieal Corporation, acorporation of Virginia Application February 27, 1952, Serial No.273,758

4 Claims. (Cl. 73-432) This invention relates to a method of determiningvarious properties of metals and alloys having definite polyhedralstructure.

Various properties of metals having polyhedral structure and capable ofdeep drawing are related to each other and to the surface roughness ofthe metal. These properties include tensle strength p. s. i., elongationpercentage in 2", and grain sze. Such metals include austeniticstainless steels, low alloy steels, deep drawing grades of aluminum,copper and copper base alloys. By way of description the followngspecification will be directed to determining grain size of copper basealloys, but the invention is not limited to these alloys, and can alsobe employed for determining the other factors mentioned.

F abricators of brass, bronze and other copper base alloys desire tosecure material from the rolling mills which will require the leastamount of polishing to produce a high lustre on the finshed product. Theideal material is that having the smallest average grain size which canbe drawn or otherwse formed without breakage. The smaller grain sizeresults in the smoothest formed surface in the fabricated product. Assome tolerances must be allowed for manufacturing varables, thespecifications are generally establshed as the minimum grain size whichthe fabricator can use with an upper figure or spread to allow fl suchmanufacturing variables.

Grain size has heretofore been determined by one of several methods.When determined by estimate, the specimen is viewed in a microscope at amagnification of 75 diameters and compared with pictures of standardgrain sizes published by the A. S. T. M. A second, and more accurate,method is to count the number of grains intersecting a line of knownlength. This is known as the Heyn intercept method. Both of thesemethods are open to the objection that they depend upon the skill of theoperator. A more accurate method is the Jeffries modified pianimetricmethod. This requires counting of grains within an area and is,therefore, more cumbersome than either of the other methods.

My invention comprises a method of measuring grain size of these metalsand alloys by mechanical means whereby more accurate results areobtained and in which the accuracy of the results does not depend uponthe skill of the operator. I have discovered that upon stretching, thesurface of a sample of a rolled alloy becomes roughened in proportion tothe size of the grains it contains and that a curve of surface roughnessplotted against grain size is a substantially straight line. 1,therefore, stretch a specimen of the material a predetermined amount,measure the roughness of the surface by apparatus available for thatpurpose, such a profilometer, and then convert the value obtained tograin size by means of charts or tables made available from experimentaldeterminations.

In practicing the invention a specimen strip is first cut from therolled sheet. The specimenis of a uniform wdth, and of a width that canbe handled in the various apparatus. In actual practice I have employedspecimens inch by 5 inches.

The specimen is marked with a one inch or two inch gauge length tofacilitate determination of percentage of stretch. The specimen is thenstretched to the desired percentage in any suitable stretchingapparatus. It is then placed in a Profilometer, an apparatusmanufactured by Physicists Research Corporation, to quantitativelymeasure surface roughness. This apparatus traces the surface andaverages the roughness as the root means of the square of the distancefrom the valleys of the surface to the hilltops." It is indicated on thedial of the instrument as microinches R. M. S. (root means square). Anyother apparatus capable of measuring the surface rough ness may be usedin place of the Profilometer.

By means of previously prepared charts or tables, the value thusobtained may be converted to grain size. In the accompanying drawing Ihave shown a chart prepared from data I have determined in which surfaceroughness in microinches, R. M. S. is plotted against grain size.

Curve 1 represents the values of a copper base alloy that has beenstretched 20 percent; and

Curve 2 the values of such an alloy that has been stretched 30 percent.

By way of example with 20 percent stretch, if the surface roughnessreading is 82 microinches, as indicated by point 3, the grain size is 60microns. Similarly with a 30 percent stretch, and a surface roughness of68 microinches, as indicated by point 4, the grain size is 40 microns.

As a result of the experimental work performed, I have determined thatthe gauge of copper base alloys has little etcct on surfaceroughness-grain size relationship. The procedure herein described isbest suited for grain sizes below 080 mm. but is satisfactory up to .140mm. The relationship does not held good for very thn metal or relativelythn metal with very large grain size, but these consttute a very minorpart of commercial production of copper base alloys. Separate curves ortables may be used to advantage for material over 100 in. thck and ander.006 in. thick. I have also found that small variations in the amount ofstretch do not appreciably affect the results.

Experiments have been made in which the specimens were stretched 40percent to secure maximum roughness. Many samples broke before beingstretched to that point. A 30 percent stretch has been found to besatisfactory in most instances; The exceptions to this are the verylarge grained, relatively thn sheets referred to above. I have alsofound that for practical purposes a 20 percent stretch gives reliableresults.

Instead of grain. size the usefulness of an alloy of the type discussdfor fabricating is determined by its tensile strength p. s. i. or anelongation percentage in 2. These properties all indicate the ductiltyof the metal, and the amount of polishing it will require afterfabricating. By means of tables grain size may be translated into eitherof these values or these values may be translated into grain size. Withcopper base alloys diferences in composition of the alloy anddifierences in gauge have little etect on the relation of surfaceroughness to grain size.

In determining properties other than grain size with metals or alloysother than copper base alloys, and of diflerent gauges, separate chartsor tables must be used to convert the Profilorneter readings to thedesired values.

Among the many advantages of the invention are its simplicty ofoperation, minimizing of variation When work is done by differentoperators, relatively large area of specimens covered as compared tomicro examination,- and area traced not arbitrarily selected by theoperator. I have also found that it makes substantially no 2,735,304Patented Feb. 21, 1956 7 diiferenc whether the stretching is done in thedirecti0n of the grain or across the grain.

I claim:

1. The method of determining the grain size of a test sample of a rolledmetal haviriga polyhedral structure whch comprises stretching the testsample by a predetermined amount ancl quantitatively measuring thesurface roughness of the sample after subh stretching, whereby the grainsize of such test sample may be determined by cunvertng the so measuredsurface roughness nto grain size by means of experimentally determineddata on the relation between grain sizes and corrcsponding surfacerouglmesses of rolled spcmens of such a metal whch have been stretchedsuch predetermined amount.

2. The method according toelaim 1, in which the test sample is stretchedsubstantially 20%.

-s. m method according claim 1, in which the u:

sample is strelched substantially 30% 4. The method aecording to claim1, in which the metal is a copper base alloy.

Reference: Clted in the file of this patent UNITED. STATES PATENTS CrossApr. 9 1946 UI'HER REFERENCES Grain sm, Symposium held during theSixteenth Annual Conventon of the Society in New York city the

1. THE METHOD OF DETERMINING THE GRAIN SIZE OF A TEST SAMPLE OF A ROLLEDMETAL HAVING A POLYHEDRAL STRUCTURE WHICH COMPRISES STRETCHING THE TESTSAMPLE BY A PREDETERMINED AMOUNT AND QUANTITATIVELY MEASURING THESURFACE ROUGHNESS OF THE SAMPLE AFTER SUCH STRETCHING, WHEREBY THE GRAINSIZE OF SUCH TEST SAMPLE MAY BE DETERMINED BY